'use strict';
let single_element = function(collection){
    var isEven=i=>i%2===0;
    var indexEvens=arr=>arr.filter((value,index)=>isEven(index+1))
    let arr=indexEvens(collection)
    let repeat=[]
    for(let i=0;i<arr.length; i++){
        if(arr.indexOf(arr[i])!=i)
        repeat.push(arr[i])
    }
    return arr.filter(x=>!repeat.includes(x))
};
module.exports = single_element;
